Worm control programs are an important part of farm management on most sheep properties. Each state has detailed worm control programs designed to manage worms to minimise production losses and delay drench resistance.

Two broad programs encompass the winter rainfall regions where Teladorsagia (brown stomach worm, previously known as Ostertagia) and Trichostrongylus spp (black scour worm) are the important worm species present; and the summer rainfall regions where Haemonchus contortus (barber’s pole) is also important. Local variations in climate and management make a significant difference to worm control. Seek advice from a veterinarian or animal health adviser to design a program specific for your property. A good program is flexible enough to accommodate climatic and seasonal fluctuations.

Winter and non-seasonal rainfall regions of southern Australia

Strategic drenching: time drenching to minimise drench frequency
Either one or two summer drenches should be given. These drenches control worms for the rest of the year. The downside of summer drenching is that it contributes to drench resistance. For this reason, give the first drench when pastures dry out, but before late December, regardless of region. In lower rainfall areas, or in dry years, monitor worm egg count (WEC) as drenching may not be required. Always monitor WECs of all mobs to see if a second drench is required in February.

On annual pastures in Western Australia, ewes should NOT be routinely drenched in summer. Do a worm egg count in March/April to determine the need to drench, as egg counts often rise in late summer. Read the WA Department of Agriculture and Food Fact Sheet 11/205: Sheep worms: summer-autumn worm control at www.agric.wa.gov.au (search for “drench”) or visit www.wormboss.com.au for specific advice (see also signposts in procedures 11.2 and 11.3).

The other ‘must do drench’ is the weaning drench for lambs. Drench and wean lambs off Merino ewes at 14 weeks . In some circumstances meat breed lambs benefit from staying on meat breed ewes slightly longer but all lambs benefit from drenching at this time. It is normally not necessary to drench at lamb marking if ewes are lactating well and lambs are weaned at 14 weeks.

Pre-lambing drench for ewes
If ewes are in good condition and grazing recommended pasture, then pre-lambing drenching is usually not necessary, especially with spring lambing flocks. If ewes are less than condition score 2.5 at lambing and grazing short feed on heavily contaminated pasture, pre-lamb drenching on the point of lambing may be justified. WEC monitoring is useful to determine if drenching is necessary. Prime lamb ewes, where lambs remain on ewes for more than 13 weeks, may benefit from pre-lamb drenching, partly to reduce pasture contamination for lambs.

Extra drenching
Additional drenching should only be done on information provided by WEC monitoring. Ideally, adult sheep need only 1–2 drenches per year and weaners, 2–3 drenches per year. Sheep producers exceeding this frequency should seek expert advice.

Worm egg count monitoring
WEC monitoring is done to decide on non strategic drenching and summer drenching. Monitoring is also carried out before and after drenching to check on drench efficacy.

Grazing management
The aim of grazing management is to provide young sheep that are most vulnerable to worms, with the pastures with lowest contamination. Prepare weaning paddocks by grazing with cattle for at least 6 months, or with smart grazing (see WormBoss: www.wormboss.com.au/ ). Alternatively, use wethers to prepare weaning areas for at least 6 months before lambs are weaned. Ideally, graze weaners on a second ‘safe’ paddock the following winter. Intensive grazing rotations will not necessarily reduce contamination with brown stomach worm or black scour worm. Search the MLA website for the fact sheet on Low-worm risk pastures for sheep.

Selecting sheep with low worm egg count (and low dag score)
Research shows that long-term selection for sheep with low WECs (formerly called faecal egg counts) can reduce pasture contamination and, possibly, drench frequency. Integrate with selection for all important wool and meat traits. Selection should also be targeted at reducing dag score as selection just for low WEC will not necessarily reduce dagginess.

Nutritional management
Research shows that sheep with good nutrition manage worm burdens better. Maintain sheep at condition score targets.

Timing of management events and systems
Spring lambing is an important driver of profitability in winter rainfall regions. Generally, late winter–spring lambing flocks have better worm control because ewes have better nutrition during lambing, although weaners have a higher risk in their first winter because they have not been exposed to many worms as a lamb. Wean lambs at 14 weeks for Merinos and slightly later for meat breeds. When considering flock structure, wethers are an important management tool to control worms, especially if no cattle are run on the property.

Summer rainfall regions where barber’s pole is the major worm

The program will vary between season, drench resistance status and grazing management. Monitoring WECs is critical to determine when drenching is required. Both barber’s pole and scour worms need to be considered.

Control of barber’s pole worm
The program required will depend on resistance status. Unfortunately, the key drench closantel is no longer effective on more than 60% of properties so careful selection of drenches is important. The barber’s pole season usually starts in October and extends to April on the tablelands. Time the first drench for late October to coincide with new infective larvae becoming available on pasture. Additional drenches may be required in late December and late February, or more often in warm wet seasons.

Closantel used to be the preferred drench but with resistance widespread, alternative drenches must be used to control barber’s pole over this time. Other options include combining closantel with a broad-spectrum drench or naphthalophos 3 weeks later, or using moxidectin (if effective) as an alternative to closantel. Another option includes using an effective broad-spectrum drench and/or naphthalophos with a move to clean pasture. Always monitor to see if these drenches are required and consult your veterinary or animal health adviser to fine-tune plans appropriate for your property. Relying solely on long acting products such as capsules or long acting drenches may increase selection for drench resistence.

Additional drenches
Additional drenches that may be required for broad-spectrum control of brown stomach worm and black scour worm include pre-lamb drenching (monitor) of ewes and a weaning drench for lambs at 14 weeks after the start of lambing. Additional drenches for lambs should always be based on worm tests over the following late autumn and winter.

Faecal worm egg counts (WEC)
WEC monitoring is done to decide on non strategic drenching and summer drenching. Monitoring is also carried out pre and post drenching to check on drench efficacy.

Grazing management
The aim of grazing management is to provide young sheep that are most vulnerable to worms with the pastures with lowest contamination. Prepare weaning paddocks with cattle for 3-6 months (depending on time of year) or with smart grazing (See WormBoss at www.wormboss.com.au/). Alternatively, use wethers to prepare weaning areas for at least 6 months before lambs are weaned. Ideally, graze weaners on a second ‘safe’ paddock the following winter. Research indicates that barber’s pole can be controlled effectively by rotational grazing where the rotation length extends to at least 50 days. This is useful in summer when barber’s pole larvae survive for about 50 days. Search the MLA website for the fact sheet on Low-worm risk pastures for sheep.

Selecting sheep with low worm egg count (WEC)
Research shows that long-term selection for sheep with low worm egg counts can reduce pasture contamination and possibly drench frequency. Integrate selection pressure with selection for all important wool and meat traits. This strategy is most useful for control of barbers pole.

Nutritional management
Sheep with good nutrition manage worm burdens better. Maintain sheep at condition score targets. Research in the New England region indicates that protein supplementation on poor quality pasture can have a significant effect on worm control in lambing ewes.

Timing of management events and systems
As for winter rainfall regions.